The purpose of this project is to build a super strenght, waterproof messenger bag to keep your gizmo away from dangers when biking.

Step 1: Materials

sandbag
a broken dog chain
2 pieces of velcro
tape
used belt

Step 2: Prepare the Sandbag

- clean the inside of the bag using water (a lot of remaining sand will be inside)
- make sure that the bag is dry (inside and outside)
- choose the worst side of the bag (the dirty one)
- cut out half plastic layer (see the first image).
- keep the cut part for next steps.

Step 3: Add Velcro to Edges

- Add velcro to edges.
- Before attaching to the sandbag make sure that when the bag is full of things, the two sides of the velcro will match.

NOTES: I used self-adhesive velcro. If the adhesive is not so strong you can use some staples. If you use staples, keep in mind to waterproof the staples putting tape over them.

Step 4: Add the Chain to the Bag

- put the chain on the center of the bag (where the bag will fold). Check that the chain is longer than the size of the bag (first photo)
- cut out from the remaining piece of plastic a rectangle wider three time than the chain anl longer as the bag
- put the plastic rectangle over the chain (third photo)
- attach the plastic rectangle to the bag using tape.
- fix all the holes on the bag using the same tape (last photo)

Step 5: Add the Belt to the Bag

- attach the belt to the chain on both sides
- close the ends of the belt with a bolted joint
- try to wear the bag (empty and full) and adjust the lenght of the belt until you feel confortable

Step 6: Decorate

- if you don't like in plain color you can decorate your bag
- i used spray colors and some DIY paper stencil. Spray paint works very well on this plastic.